The present invention relates generally to laser optical detection systems, and specifically to a monolithic area array of optical elements shielded by a mechanical or electronic shutter designed for low background laser ranging.
Laser rangefinders detect the range of remote objects by transmitting a pulse of light and detecting the echo return signal. The time-of-flight is measured to yield the range or distance between the target and the rangefinder. Exemplary of such systems are the devices disclosed in the following U.S. patents, which are incorporated herein by reference:
U.S Pat. No. 4,380,391 issued to Buser et al;
U.S. Pat. No. 4,380,755 issued to Endlicher et al;
U.S. Pat. No. 4,498,105 issued to Crawshaw;
U.S. Pat. No. 4,518,256 issued to Schwartz; and
U.S. Pat. No. 4,531,156 issued to Nishizawa et al.
Schwartz discloses an optical radar which includes a laser transmitter and an optical receiver. The receiver is described as an array of detectors which serve to divide up the field of view of the receiver into sectors about the boresight of the radar. Range is determined using the range bin channels.
Buser et al discuss a system for laser ranging and target identification and speak of observing the time broadened reflected signals that result from integration of the finite depths of the targets. Endlicher et al are concerned with a monolithically integrated two-dimensional image sensor having an array of sensor elements disposed in rows and columns connected by respective row and column lines. In Crawshaw a CCD imager is formed with an A register exposed to illumination and has B and C registers masked from illumination. Nishizawa et al disclose a solid state image pickup device which has an electronic shutter function.
Laser ranging systems use avalanche photodiodes as the sensing elements for returned signals. More recently, photodiodes coupled to charge coupled device (CCD) storage registers have been used as the detector elements. Both types of devices can be fabricated into monolithic linear arrays. Formation of area arrays has required hybrid assembly. Some schemes have been proposed for forming monolithic area arrays, but, these methods require complex manufacturing processes and are limited to a few rows of detectors.
In view of the foregoing discussion, it is apparent that there currently exists the need for large area detector arrays for laser ranging. The present invention is intended to satisfy that need.